1. Field of the Invention
This disclosure relates to a sealing and/or fastener assembly that is pre-assembled with a removable mandrel.
2. Description of the Related Art
A threaded insert is a fastener assembly that is typically installed into sheet (i.e., thin) material. The threaded insert is comprised of a collar and a nut member where the collar and nut member are fixed relative to each other. The collar is generally swaged into an opening of a structural workpiece. The nut member is configured to receive an externally threaded component, for example a bolt or a screw, after the insert has been secured into the structural workpiece. One type of threaded insert is described in detail in U.S. patent application Ser. No. 10/928,641 and in U.S. patent application Ser. No. 10/965,233. The disclosed threaded inserts are installed by collapsing a portion of the collar onto the structural workpiece and contemporaneously, radially expanding another portion of the collar into the opening of the structural workpiece using an installation tool and mandrel.
The mandrel performs the radial expansion process. The mandrel must be of the proper size to achieve the correct amount of radial expansion. Thus, a large variety of different sized mandrels must be kept in stock for different sized openings and/or for rework procedures. When installing threaded inserts and/or nut plates into openings of various sizes, the mandrel must be removed from the installation tool and replaced with the proper sized mandrel. This tedious and time-consuming process may occur numerous times for each specific installation.
A nut plate is comprised of an attachment member coupled to a nut member in contrast to a threaded insert, the nut plate permits the nut member to float or move relative to the attachment member. The attachment member can be a plate, a collar, a barrel, or some other structure. A nut plate in which the attachment member is a plate is installed by riveting the plate to the structural workpiece.
Another type of nut plate in which the attachment member is a collar is installed by radially expanding a portion of the collar into the opening of the structural workpiece using the above-described mandrel. The radial expansion creates a high interference fit between the collar and the structural workpiece that allows the nut plate to resist torque and axial push/pull-out. In addition, the radial expansion of the collar into the opening may induce compressive residual stresses into the surrounding material of the structural workpiece. The compressive residual stresses may increase the fatigue performance of the structural workpiece in the vicinity of the opening. A nut plate that is installed via the radial expansion method eliminates satellite holes that are required for riveted nut plates. The satellite holes can be initiation points for fatigue cracks.
Both the threaded inserts and nut plates may or may not be sealed. For example, sealed threaded inserts and nut plates may be used in fuel tanks or other areas that may be exposed to fluids. In the sealed embodiment, a cap or dome fits over the nut member of the threaded insert or nut plate. With respect to nut plates, the cap is typically attached after the nut plate has been installed into the opening of the structural workpiece. However for threaded inserts, U.S. patent application Ser. No. 10/965,233 discloses a cap that is pre-assembled with the collar and nut member of the threaded insert.
There is a need for a lightweight nut plate that can be installed quickly and efficiently into the structural workpiece.